Stereo-sound reproducing device



Dec. 22, 1964 R. E. PFISTER STEREO-SOUND REPRODUCING DEVICE Filed Nov. 2, 1962 INVENTOR.

le/zigza United States Patent Office 3,162,728 Patented Dec. 22, 1964 3,162,728 STEREO-SOUND REPRODUCING DEVICE Robert E. Plister, 1170 Logan Ave., Elgin, Ill. Filed Nov. 2, 1962, Ser. No. 234,965 1 Claim. (Cl. 179-4) The present invention relates in general to improvments in sound reproducing equipment and is more specifically concerned with improved stereo-type of sound reproducing apparatus, such as a stereo-record player, having remote speaker means selectively connected with one output channel and including novel means for eliminating channel interference and extraneous record surface noise.

In known stereo-type sound reproduction, the inactive output transducer or speaker has a tendency to emit sounds of channel interference and spurious record surface noises. This is particularly annoying when one considers that in a system intended for childrens use, the records will accumulate a certain amount of surface noise over a short period of time. This surface noise, when present in the inactive audio frequency transducer would have a detracting effect upon the active audio frequency transducer were it allowed to exist. In order to eliminate such unwanted sound, applicant has provided novel means to decrease the input gain to the inactive audio frequency amplifier and it is one of the objects of the invention to accomplish this result.

Another feature of this invention is the effective removal of so-called cross channel modulation. The novel means provided herein effectively removes this type of unwanted sound and is one of the objects of this invention.

The invention also contemplates the provision of a modified stereo-record player amplifier system having therein means to separate the audio output of one of the two stereo channels and deliver it to a remotely placed audio transducer connected into one channel. As one example of a use of this arrangement the remotely placed audio transducer may be arranged in the body of a dummy representative of, for example, a doll or animal, and of a type and character to match the story or sound produced in the selected channel. The audio output of the other channel is delivered to the usual audio frequency transducer of the system and, if desired, the remote amplification can be terminated at will and the audio output formerly fed to the remote transducer can be directed to the secondaudio transducer in the player. Another object of the invention is to provide such a system.

Another object is to provide a stereo-record player and remote audio transducer combination of the character referred to.

The structure by means of which the above noted and other objects and advantages of the invention are attained will be described in the following specification, taken in conjunction with the accompanying drawings showing a schematic representation of a stereo-record player and representative illustration of electronic components and a character representation associated therewith for carrying out the features of the inventionl Referring to the exemplary disclosure of the invention shown in the accompanying drawings, the stereo-system includes any conventional type of stereo-record player including a stereo pickup cartridge 11 and conventional potentiometers i2, 13 arranged in input lines 14, 15 to audio frequency amplifiers 16, 17 respectively. The output from said amplifiers is connected to the series hook up output audio frequency transformers 18 and 20, 19 and 21 respectively. In the present instance each transformer 18, 19, 20 and 21 has a secondary impedance of about 3.5 ohms.

An audio frequency transducer 44 is connected by leads 22 to the secondary of transformer 20 whereas the secondary of transformer 18 has a pair of leads 23 connected to a 1.3 volt lamp 24 for a purpose to be explained presently. Similarly, leads 25 connect a second audio frequency transducer 26 to the secondary of transformer 21, and leads 27 connect the secondary of transformer 19 to a 1.3 volt lamp 28 for purposes also to be explained presently. The inclusion of these low voltage lamps, one in each channel circuit, results in no noticeable loss of gain. A pair of ganged switches 29 arranged in the input circuits to the transformers affords means to effectively make the lamps non-functioning in instances of use when their function is not desired.

Leads 2 5 to audio frequency transducer 26 includes a jack switch 31 into which may be inserted a jack 32 having flexible leads 33 of any desired length connected to an auxiliary audio frequency transducer 34- which preferably is enclosed in the body of a doll or other character representation 35. Preferably, and for full effect, the character representation 35 is in substantial conformance with the subject of the stereo recording. The effect of animation by use of the doll representation may be enhanced by providing the body of said representation with an opening 36 to permit the insertion of the operators hand or fingers for manipulating features of the representation.

In use, insofar as described, only one channel of the stereo-record player is audible at any one time. For example, the channel connected with transducer 21 may be utilized to emit background sounds or to be inaudible, whereas the channel including transducers 26 or 3 3 may emit spoken words, vocal accompaniment or be silent. When only one channel is active it is the purpose of this invention to eliminate all channel interference such as extraneous record surface noises and cross channel modulation normally emitted from the audio transducer that is not active.

To accomplish this each lamp 24, 28 has associated with it so as to be influenced by the degree of light emitted from the related lamp, a cadmium sulphide variable resistance type photocell 37, 38 respectively. These photocells have a dark resistance of approximately 10 megohms which lowers to about 200 ohms in strong light. Preferably, a reflector 39 is associated with each lamp and each lamp-photocell assembly is enclosed in a light-tight case 41 for maximum light absorption by the photocell. The output of one photocell, for instance photocell 37, is placed across the input circuit of audio frequency amplifier 17, through lead 4-2. The output of the other photocell 38 is placed, by lead 43, across the input circuit of audio frequency amplifier 16.

Because each photocell perceives light only from the lamp with which it is associated, the resistance varies inversely with the light strength. Therefore, the stronger the light the lower the resistance of the related photocell. Now, because the photocell 37, for example, is connected across the input to amplifier 17, there is a decrease in input gain to this amplifier when the output of audio frequency transducer 44 is active and visa versa. ince the dark resistance of the photocells is high, their connection with the input to the respective amplifiers does not affect the signal so long as no modulation is present on the opposite amplifier. When audio is present in a given transducer and the resistance of the photocell is reduced, a reduction of gain in the other channel is noted. In this manner any interference and spurious record surface noise in either channel is completely eliminated while the other channel is active, the exact degree of elimination being dependent upon the percent of modulation present in the opposite channel. Photocell saturation occurs at a level just below normal room volume hence, as long as the volume controls 12, 13 are in a normal listening position, or above, the system will function satisfactorily. At any level less than normal, cross channel interference and reco d ce noise is of no on equen It might be noted also that due to the slightly delayed return response of the lamp and photocell at saturation, input to the opposite amplifier is completely attenuated not only during modulation of the opposite amplifier but also during short pauses between words and phrases.

It will be apparent that when either audio frequency transducer is active, the opposite transducer is inactive and that substantially all unwanted noise normally emitted from the inactive transducer is eliminated and that for normal speech, audible in one channel, the opposite channel will remain silent.

Although applicant has disclosed herein a representative embodiment of the invention, it is to be understood that the disclosure is by way of illustration and not limitation and that the invention is capable of embodying a variety of modifications. in detail structure and application without departing from the spirit and scope of the appended l im What I claim and desire to secure by Letters Patent of the United States is:

In a stereo-record player of the type including a dual audio frequency signal amplification system, an audio frequency amplifier in each system, a pair of audio frequency transformers connected in series to the output of each audio frequency amplifier speakers, one connected to the output of one transformer of each pair of transformers, a photo-cell connected to the input circuit to the audio frequency amplifier in one amplification system, a light source for said photo-cell connected to the secondary of the other audio frequency transformer in the pair of transformers in the other amplification system effective when the speaker in said other amplification system is active to attenuate signal input to the first named audio frequency amplifier, and switches in the circuits to said light sources operative to shunt the respective transformers to render the respective light source ineffective.

References Cited by the Examiner UNITED STATES PATENTS 2,110,358 3/38 Dreisbach 179-1 2,205,447 6/40 Wallace et a1 1791 2,247,329 6/41 Deitz 179-1 2,335,575 11/43 Bierwirth 179-1 2,379,768 7/45 Van Wynen 179-170.6 2,495,809 1/50 Graham 179-1 2,748,201 5/56 McMillan 33084 2,839,616 6/58 MacMillan 330-59 3,020,488 2/62 De Miranda et al. 330-59 3,047,670 7/62 Gardner 179-1 3,079,463 2/63 Feldman 1791.5

ROBERT H. ROSE, Primary Examiner. 

